I recently acquired a real rust bucket outside and inside (along with mice nest). Interestingly enough, all of the tubes in this AK40 are good. Well, if my TV-7 D/U had a FAIR/GOOD/EXCELLENT meter, they'd be fair. The Cunningham CX-380 has a white patch on the inside of the getter. It also tests FAIR and works fine in an operating AK-55C. If it had truly gone-to-air, would it still work?

The getter flash on the inside of the glass is thinnest around the edges, and generally that thinnest perimeter portion visibly oxidizes first if the tube is gradually going to air. I'm not sure why the center (thickest portion) of the getter would appear white before the edges, but if the tube works, I'd say 'use it.' If it truly is going to air, you may soon get a purple light show inside the tube ... keep an eye on it. In any case, 80s are easy to find.R/ John

When air ionizes in a partial vacuum, it gives a characteristic bluish-violet-pinkish color light. If you see that inside or around the plates, time to retire the tube. Should it arc over, it could destroy the power transformer and that is a lot more difficult to replace than the tube is.

When a tube goes completely to air it will often still have filament or heater continuity. However, when you power it up, the filament(s) or heater(s) will not glow because the air removes the heat too fast. For the same reason, the bulb will heat up very quickly. Of course it will not work. Such tubes should not be operated more than necessary to see that they are bad; if the filament or heater cannot reach normal operating temperature, the current it draws will be considerably higher than normal. This can also damage transformers and other components.

Over the years, a number of different getter materials were used in tubes, some of which have different colors and appearances. While a milky white spot on tubes of more recent manufacture is usually a sign of fatal damage, you can't always go by that with earlier tubes.

_________________"Hell, there are no rules here--we're trying to accomplish something!"

"Over the years, a number of different getter materials were used in tubes, some of which have different colors and appearances. While a milky white spot on tubes of more recent manufacture is usually a sign of fatal damage, you can't always go by that with earlier tubes."

TRUE for signal tubes like 01-A's but not for rectifiers that I have ever seen. Should have NO white areas on the glass inside.Mark Oppat

See http://www.tubebooks.org/file_downloads/Getter_Material.pdf There were seven or eight different primary materials used in tube getters, and they were sometimes compounded together so there are really quite a few possibilities. It does not appear there were special precautions for ordinary high vacuum rectifier tubes, though they did have to avoid certain kinds of getters in tubes which contained mercury vapor or other gasses by design. Also, certain types of getters were avoided in higher power (transmitting) tubes.

_________________"Hell, there are no rules here--we're trying to accomplish something!"

I once dug an A-K 40 out of the sands of Cape-Cod... The steel case was in crumbs, salvaged the medallion. All the tubes were good but there was visual evidence that salt water was in the bases. The 280 was the clincher, apparently the 280 went to air while under water and was 1/2 full of sea water. I kept the tube for years but the water eventually evaporated. First full wave liquid rectifier

There were mechanical precautions for the getter device. It must not blast the getter material during firing against the press or any mica. It will or would eventually, cause the tube to fail from electrical leakage. I have found a couple of leakage failures, brightly flashed across the press..

Getters are interesting. Many years ago I got a small can of Barex getters with a date of March 1939 stamped on the label; they are the same tab style as the getter shown at top right in the 1st page photo of the article Chris108 posted. The can had been opened long before I got it and was partially empty, but I wondered if they might still yield a usable getter flash. So during some other lab work a couple years ago I spot welded one to a nickel lead in an experimental glass tube, put it on the vacuum system manifold and pumped it down to around 3E-5 Torr, tipped it off, and tried firing it using a small induction heater. Amazingly, it yielded a reasonable flash on the glass. Not something one could count on for reliable gettering, but still quite interesting ...R/ John